A refracting telescope has clear aperture and focal length (so it works at )

PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Fourier optics and image formation · Fourier optics and image formation

What an Instrument Can See, Ch The transfer function of an imaging system

Problem

A refracting telescope has clear aperture

D = 100\ \mathrm{mm}

and focal length

f = 800\ \mathrm{mm}

(so it works at

f/8

), used at

\lambda = 550\ \mathrm{nm}

. Light is detected incoherently by a camera at the focal plane. For a slow (large

f

-number) system the image-side numerical aperture is well approximated by

\mathrm{NA} \approx 1/(2N)

, with

N = f/D

the

f

-number. ((a)) Find the coherent and incoherent cutoff spatial frequencies at the image (focal) plane, in cycles per millimetre. ((b)) State the largest camera pixel pitch, in micrometres, that satisfies the sampling theorem for the irradiance image formed by this telescope.

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